class DigitalClock():
    # 数字时钟
    def __init__(self, hour=0, minute=0, second=0):
        """
        初始化数字时钟的时间。
        
        :param hour: 小时，默认为0
        :param minute: 分钟，默认为0
        :param second: 秒，默认为0
        """
        self.hour = hour
        self.minute = minute
        self.second = second

    def set_time(self, hour, minute, second):
        """
        设置时间。
        
        :param hour: 小时
        :param minute: 分钟
        :param second: 秒
        """
        self.hour = hour
        self.minute = minute
        self.second = second

    def run(self):
        """
        走字
        """
        self.second += 1
        if self.second == 60:
            self.second = 0
            self.minute += 1
            if self.minute == 60:
                self.minute = 0
                self.hour += 1
                if self.hour == 24:
                    self.hour = 0

    def display_time(self):
        """
        显示当前时间。
        
        :return: 当前时间的字符串表示
        """
        return f"{self.hour:02}:{self.minute:02}:{self.second:02}"

# 示例用法
if __name__ == "__main__":
    clock = DigitalClock(23, 59, 58)
    print(clock.display_time())  # 输出: 23:59:58
    clock.run()
    print(clock.display_time())  # 输出: 23:59:59
    clock.run()
    print(clock.display_time())  # 输出: 00:00:00
    clock.run()